Polyimide (PI) is one of the most widely used high-temperature polymers. PI possesses an excellent thermal property, mechanical property, and flame/chemical resistance and it has been extensively used in the aviation, automotive, aerospace, and electronic industries (see Maier, G., Prog. Polym. Sci. 2001, 26, 3).
A large number of new PIs with unique properties have been introduced for various industrial and consumer product applications since their commercializations at the beginning of the 1960s (see Kharitonov, A. P.; Taege, R.; Ferrier, G.; Teplyakov, V. V.; Syrtsova, D. A.; Koops, G.-H., J. Fluorine Chem. 2005, 126, 251, and Ameduri, B.; Boutevin, B., J. Fluorine Chem. 2005, 126, 221, and Rusanov, A. L.; Komarova, L. G.; Likhatchev, D. Y.; Shevelev, S. A.; Tartakovsky, V. A., Russ. Chem. Rev. 2003, 72, 899).
General synthetic methods of PIs have been well developed, including the step of condensation reaction between diamines and dianhydrides. However, PI, particularly aromatic PI, has encountered numerous processing difficulties due to its poor solubility in organic solvents. As a result, PIs are usually synthesized in-situ by forming soluble poly(amic acid) intermediates from the reaction of diamine and dianhydride at low temperatures during their first-step of syntheses, casting the poly(amic acids) as films, and in the final step, conducting ring-closuring imidization at high temperatures (>300° C.) to remove water and the solvent. In order to improve the solubility and processing capability of PIs, some structural modifications introducing bulky groups or flexible chains such as —O—, —SO2—, —C═O, —CF3, —CH3 into the backbone or side chain of PIs have also been demonstrated. (see Eastmond, G. C., Paprotny J., React. Funct. Polym. 1996, 30, 27).
In this present invention, we uncovered a new synthetic process for PIs using a sequential self-repetitive reaction (SSRR), especially as a one-pot process by bringing together poly(aryl carbodiimides) (p-CDI) from aryl diisocyanates and o-ester acids from dianhydrides. The raw materials for forming PIs are dianhydrides and common diisocyanates can also be used with a CDI catalyst as the sources for p-CDIs through poly-condensation reactions.